Natural or synthetic fabrics can be waterproofed by laminating or coating them with elastomeric water-impervious materials comprised of, for example, polyvinyl chloride, styrene-butadiene, silicone, polyurethane or latex. However, apparel coated with such waterproof materials are uncomfortable to wear, as human perspiration is not able to evaporate through such material. Accordingly, considerable efforts in the past have been directed to the development of apparel that could simultaneously “breath” and be “waterproof”. These efforts culminated in the discovery of a novel breathable waterproof film by R. L. Gore, and trademarked as Gore-Tex™. (see, for example, U.S. Pat. Nos. 3,953,566 and 4,194,041).
The original Gore-Tex™ invention is a microporous technology based on a process of rapidly stretching heated PTFE (polytetrafluoroethylene) film to create a microporous structure, creating pore openings that are sufficiently large to allow water vapor to pass, but not liquid water, due to strong capillary forces that prevent the passage of liquid water. Subsequent to the Gore-Tex™ invention, other waterproof breathable films based on micropores have been developed. These films include expanded polyethylene, PVC, crushed foam coatings, or coatings that become porous due to drying, curing, or salt or solvent extraction. However, the drawback of microporous films is that the micropores can become clogged due dirt or other substances, reducing water vapor transmission.
Accordingly, researchers have developed monolithic films without micropores, such as hydrophilic thermoplastic polyurethane films (TPU), that allow rapid water vapor diffusion, but not liquid water through the film (see, for example, U.S. Pat. No. 4,367,327). These new PTU films are more cost effective and have better physical properties, including high stretch, than the Gore-Tex™ PTFE films. Also, TPU films, can be modified to increase the MVTR (moisture vapor transmission rate) by adding, for example, a hydrophilic poly(ethylene oxide) as a copolymer component. Additionally, proprietary non-porous films such as Sympatex™, a registered trademark of AKZO Nobel Fibers Inc. of Hampton, N.H. U.S.A., are also available. See, for example, U.S. Pat. No. 5,631,074.
As all waterproof breathable films are very thin and delicate, they are usually bonded to a mechanically stronger outer fabric, generally comprised of abrasion-resistant fabric comprised of woven fibers of polyester, polypropylene or nylon, which outer fabric is treated with a so-called DWR (Durable Water Repellent) coating to prevent the outer fabric layer becoming wet and reducing water vapor transmission. The delicate waterproof breathable films are also often bonded to a fine polymer mesh scrim on the inside of the apparel laminate so as to provide mechanical protection of the film surface.
More recently, water-based polyurethane dispersions have been developed, which dispersions can be coated directly onto fabrics to make such fabrics breathable but water still resistant. Thus, the discovery of breathable waterproof fabric has spurred the use of such fabrics in various sports apparel, for example, breathable waterproof hiking/biking jackets, ski/snowboard suits, drysuits and survival suits, and other shaped articles such as tents.
The apparel industry broadly defines “breathable” as material with a WVTR (water vapor transmission rate) of at least 500 g/m2/day, and a “waterproof” material as being able to withstand a 1,000 mm hydrostatic head of water (ie. 9.8 kPa pressure) without leaking. However, modern fabrics can exhibit an WVTR of 10,000 g/m2/day or more, and a waterproof rating in excess of 10,000 mm.
Generally, breathable, waterproof fabrics are not stretchable, as the outer nylon, polypropylene or polyester woven shell does not stretch. For some applications, such as drysuits, having a 4-way stretch shell would be advantageous. For example, current breathable drysuit shell fabric does not stretch, resulting in a bulky garment, as the user must don and doff the suit without being able to stretch it. Those skilled in the art will recognize that it is technically feasible to laminate a stretchable breathable waterproof film, such as TPU, to a 4-way stretchable fabric comprised of, for example, a polyester, polypropylene or nylon woven fabric containing 10-20% elastic synthetic fibers, which fibers have been woven into both the warp and weft directions. Such highly elastic synthetic fibers are typically comprised of a polyester-polyurethane copolymer, marketed under various trade names (ie. Spandex, Lycra, Elastane),
The prior art discloses breathable waterproof fabric layers. For example, U.S. Pat. No. 8,993,089 by Conolly, et. al. discloses a multi-layer fabric designed to minimize radiant heat loss, via radiation, for use in watersports and outwear apparel. The authors encapsulate a metalized layer within a laminated structure for corrosion protection, and also to minimize heat loss through conduction. However, such a design requires at least one air gap between the metal surface and the adjoining laminate layer, which they accomplish by having the metal layer span the air gap formed by the perforations of an adjoining layer. Accordingly, only the inner laminated “open area” that is perforated will act as an infrared reflective barrier. The authors also disclose an alternative approach by metalizing through the very open pore structure of an outer textile “such that the metallization coats through the air gaps of the textile onto the substrate (ie. permeable membrane layer)”. Conolly et. al. in U.S. Patent Application 2015/0305421 A1 further refine their idea of using an encapsulated metalized layer embedded within a composite structure by using a 3D warp knitting process as a fabric spacer, rather than using a thin layer of perforated neoprene, to greatly increase the surface area of the metalized layer facing an air gap, thus increasing the effectiveness of the thermal barrier to infrared radiation. However, such a design essentially creates an open-cell structure, where all cells are completely open and interconnected to each other, where any leakage or water intrusion would contact the metalized surfaces, destroying the radiative aspect of the metalized layer.
United States Patent Publication 2016/0176168 by Zhao describes a breathable multi-layer laminate comprised of monolithic core layer melt-fused on each side to a breathable skin layer, where one skin layer is glued to a woven or non-woven fabric. Such a laminate has application for a variety of uses, for example, as a protective barrier in medical applications. Zhao claims to improve upon prior art monolithic breathable films by co-extruding such films with a breathable skin layer on both sides of the core layer, and claims that such a multi-film laminate is less prone to having pin holes. Zhao modifies one or both skin layers with a filler (powder), such as calcium carbonate, which filler penetrates the skin layer to create surface protrusions, which protrusions reduce the coefficient of friction of the laminate, thus allowing the laminate to more easily unwind without tearing. Finally, Zhao claims that the disclosed laminate also improves bonding to a non-woven fabric surface, even when the hydroscopic skin layer becomes hydrated.